@yoruzora,
Is your sibling taking care of your aging parents, or are they committed to doing so?
If so, then sit this one out and let them have the extra. Care giving is not cheap and it is exhausting.
If not, then consider -- seriously consider -- how important this money is to you, and to your sibling (who, by the sounds of it, doesn't have a home of their own). If they need it more then here's a wild idea -- be the bigger person and let them have the money.